1. Field of the Invention
The present invention relates to a head position signal demodulator and a head positioning unit utilizing the demodulator, and more particularly to a head position signal modulator which generates a position signal of the head from a servo pattern and outputs the signal, and a head positioning unit utilizing the demodulator, in a magnetic disk unit which positions a magneto-resistance effect head by a rotary actuator.
2. Description of the Related Art
There is a type of a magnetic head where a record head and playback head are equipped at a specified interval along the tangential direction of a disk. For the playback head, a magneto-resistance effect head (MR head) is frequently used, and for the record head, an inductive head (ID head) is used. A magnetic disk unit has a type which positions a magnetic head in such a configuration by a rotary actuator. In this case, an inclination in the disk tangential direction occurs to the magnetic head depending on the position of the magnetic head on the disk. Because of this, a locus of the record head during recording and a locus of the playback head during playback may not match even if the magnetic head is scanning the same track. This is not good for regenerating data. Ideally the locus of the record head during recording and the locus of the playback head during playback should match.
Micro jogging is used for this control. Micro jogging is an operation for delicately adjusting the position of the magnetic head for recording and for playback, so that the locus of the record head during recording and the locus of the playback head during playback match on the same track. The magnetic head is positioned by regenerating a servo pattern which has been recorded on the magnetic disk, and controlling the actuator so that a position signal of the magnetic head which is generated according to the playback signal is maintained at a constant level. If micro jogging is performed here, the position where the magnetic head is supposed to be positioned differs for recording and for playback. Therefore in prior art, a value of the position signal to be maintained is different for recording and for playback.
This means that in a positioning control system, a control target value must be switched for recording and for playback, which made the configuration of the control system complicated. Also the relationship between the correction amount by micro jogging and the change of the position signal had to be measured for presetting the control target, which increased the number of manufacturing processes. An MR head also has such problems as thermal aspirity (TA), Barkhausen noise (BHN), baseline shift (BLS), asymmetric waveform (WA), output value fluctuation (PCOV), and asymmetric off track profile, and these problems sometimes interfere with the correct playback of servo patterns.